Published: 18 Jun 2025

ICD9: 281.0      ICD10: D51.0      ICD11: 3A01.30

Pernicious anemia, also known as vitamin B12 deficiency anemia, is a condition where your body can't absorb enough vitamin B12 from the food you eat.
This leads to a deficiency in B12, which is crucial for red blood cell production and nerve function. It's part of the broader category of "B vitamin deficiencies" because problems absorbing other B vitamins can also lead to anemia and other health issues.

Here's a breakdown:

Key Aspects of Pernicious Anemia (Vitamin B12 Deficiency):

Root Cause: Malabsorption of B12: The primary problem isn't a lack of B12 in the diet, but an inability to *absorb* it from the gut.
Intrinsic Factor Deficiency: The most common cause is a lack of a protein called "intrinsic factor" (IF) in the stomach. IF is produced by cells in the stomach lining and is essential for B12 absorption in the small intestine. Without IF, B12 can't be properly absorbed. The body may attack the cells in the stomach that produce intrinsic factor (autoimmune reaction).
Other Causes of B12 Malabsorption: While intrinsic factor deficiency is the main cause, other things can lead to B12 deficiency:
Atrophic gastritis: Chronic inflammation of the stomach lining, which reduces stomach acid and IF production.
Surgery: Gastric bypass or removal of part of the stomach or small intestine.
Intestinal disorders: Conditions like Crohn's disease or celiac disease can interfere with B12 absorption.
Certain medications: Some medications, like proton pump inhibitors (PPIs) and metformin, can interfere with B12 absorption.
Dietary factors (rare): Strict vegans who don't supplement B12.
Consequences: B12 is essential for:
Red blood cell formation: Lack of B12 causes abnormally large, immature red blood cells (megaloblasts) that don't function properly, leading to anemia.
Nerve function: B12 is critical for the myelin sheath, the protective covering around nerve fibers. Deficiency can cause nerve damage.
DNA synthesis: B12 is involved in DNA production.
Symptoms:
Anemia symptoms: Fatigue, weakness, pale skin, shortness of breath, dizziness.
Neurological symptoms: Numbness and tingling in hands and feet, difficulty walking, memory problems, confusion, depression, dementia.
Other symptoms: Sore tongue, loss of appetite, weight loss, nausea, constipation or diarrhea.
Diagnosis:
Blood tests: Complete blood count (CBC) to check for anemia, B12 levels, intrinsic factor antibody test, methylmalonic acid (MMA) and homocysteine levels (elevated in B12 deficiency).
Schilling test (less common now): Measures B12 absorption before and after giving intrinsic factor.
Treatment:
B12 injections: Bypasses the absorption problem and delivers B12 directly into the bloodstream. Usually given regularly (e.g., weekly, monthly).
High-dose oral B12: Can be effective for some people, especially if the deficiency isn't severe or if they can't tolerate injections.
Addressing underlying cause: If the B12 deficiency is due to a condition other than intrinsic factor deficiency, that condition needs to be managed.
Other B Vitamin Deficiencies:
Folate (Vitamin B9) Deficiency: Similar symptoms to B12 deficiency (anemia, fatigue). Can be caused by poor diet, malabsorption, or certain medications.
Other B Vitamins: Deficiencies in other B vitamins (e.g., B1, B2, B3, B6) can cause various symptoms, including neurological problems, skin problems, and digestive issues.

In summary: Pernicious anemia is a specific type of B12 deficiency caused by the body's inability to absorb B12, often due to a lack of intrinsic factor. It's important to recognize the symptoms and get diagnosed and treated promptly to prevent serious complications, especially neurological damage. While "pernicious anemia" specifically refers to B12 deficiency, it's important to remember that deficiencies in other B vitamins can also cause significant health problems.

Disclaimer: This information is for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.